The compartments are on this stop sign because of the heavy skew at this intersection. Only the side-street traffic is supposed to see it, so they are blocking the message from those on the main street. It is colored red so that from a distance, it just blends in with the sign. Actually, pretty ingenious way to do it. However, for those on the main street, they will only see a red octagon, which is still universal for "STOP".
